Field of the Invention
The invention relates to a protective covering, membrane or sheath for a stent delivered by a balloon dilatation catheter, such as the kind used in percutaneous transluminal coronary angioplasty (PTCA) procedures.
In typical PTCA procedures, a guiding catheter is percutaneously introduced into the cardiovascular system of a patient through the brachial or femoral arteries and advanced through the arteries until the distal end is in the ostium of the desired coronary artery. A guidewire and a dilatation catheter having a balloon on the distal end are introduced through the guiding catheter with the guidewire sliding within an inner lumen of the dilatation catheter. The guidewire is first advanced out of the guiding catheter into the patient's coronary vasculature and the dilatation catheter is advanced over the previously advanced guidewire until the dilatation balloon is properly positioned across the lesion. Once in position across the lesion, the preformed balloon is inflated to a predetermined size with radiopaque liquid at a relatively high pressure to compress the atherosclerotic plaque of the lesion against the inside of the artery wall and dilate the artery. The balloon is then deflated to a small profile, so that the dilatation catheter can be withdrawn from the patient's vasculature and blood flow resumed through the dilated artery.
In angioplasty procedures of the kind referenced above, there may be restenosis of the artery, which may require another angioplasty procedure or a surgical bypass operation. To help prevent abrupt closure, dissection, or restenosis, a physician can implant an intravascular prosthesis for maintaining vascular patency, called a stent, inside the artery at the lesion. The stent is expanded to a larger diameter, often by a balloon catheter. The stent is left in the artery, either temporarily or permanently, at the site of a dilated lesion.
The stent is delivered to the dilated lesion site by a catheter. The stent may have protuberances on its outer surface facing the patient's lumen wall. If such protuberances rub the lumen wall during delivery of the stent, they may damage the lumen wall and cause the stent to be displaced from the catheter.